Continuous method of producing a mash extract

ABSTRACT

The present invention relates to a mash extract and a continuous method of producing the mash extract by decoction mashing. The method comprises: (a) mixing a first malt enzyme source with an aqueous liquid to obtain an aqueous malt enzyme suspension; (b) separately, mixing a second enzyme source with one or more starch-containing adjuncts to obtain a decoction suspension; (c) subjecting the decoction suspension to a first heat treatment at 60-85° C. and then a second heat treatment at a higher temperature; (d) combining the heated decoction suspension from the second heat treatment with the aqueous malt enzyme suspension to obtain a mash; (e) maintaining the mash at 35-85° C. for a time; and (f) removing spent grain from the heated mash to produce a mash extract.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/301,440 filed Apr. 3, 2009, which is the National Phase ofInternational Patent Application No. PCT/NL2007/050207, filed May 14,2007, and published as WO 2007/136252, which claims priority fromEuropean Patent Application Nos. 06114264.2, filed May 19, 2006, and06114242.8, filed May 19, 2006. The contents of these applications areincorporated herein by reference in their entirety.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a continuous method of producing a mashextract by decoction mashing. More particularly, the present inventionrelates to such a decoction mashing method that employs one or morestarch-containing adjuncts as a source of fermentable sugars.

BACKGROUND OF THE INVENTION

Decoction mashing is one of the three mashing methods that are oftenwidely used in the production of bottom-fermentation beers, the othertwo methods being single infusion mashing and step infusion mashing. Theprocess typically requires three vessels: a mash tun for mash mixing, amash kettle (or copper or mash copper) for boiling, and a lauter tun (orclarifying tun) for straining. Mashing is carried out in a mash tun, andstarts at a low temperature while portions of the mash are taken out andboiled in the mash kettle and later returned to the mash tun, thusgradually raising the temperature of the entire mash. The process isusually repeated two or three times, taking two to six hours. The mashtemperature may start as low as 35° C., but more often at 45-50° C. toreach 70-78° C. at the end of the mashing process. The mash is thenfiltered in a separate vessel known as a lauter tun or in specific casesin the mash tun itself over a perforated bottom.

The fact that part of the mash is boiled is the main difference betweendecoction mashing and the other mashing methods. Because of the boiling,cell walls of the starch containing grains are destroyed. This allows aneasier access for the enzymes to the starch. As a result the efficiencyof decoction mashes is generally higher than for other mashing methods.Another advantage of decoction mashing is that grains that needgelatinising at high temperatures can be boiled separately in one of thedecoction steps. This can be useful if an adjunct such as maize, rice orrye is employed in the mash.

Decoction mashing methods employed within the brewing industry arecarried out in a batch-wise fashion.

DE-A 1 442 292 describes a batch decoction process comprising thefollowing steps:

-   i. mixing malt with water and other ingredients to obtain an aqueous    malt enzyme suspension;-   ii. mixing malt, maize grits and water to obtain a decoction    suspension;-   iii. liquefying the decoction suspension by first heating at 70° C.    for 30 minutes and subsequently heating at 95-100° C. for 10    minutes;-   iv. combining the heated decoction suspension and the malt enzyme    suspension to obtain a mash;-   v. maintaining the mash at 70° C. for 45 minutes; and-   vi. removing spent grain.    In the paragraph at the bottom of page 4 it is stated: “In order to    avoid high viscosity in the cooker, about 10% of the total malt may    be added to the maize grits”.

It would be advantageous to carry out decoction mashing in a continuousfashion. Continuous operation of decoction mashing would offer a numberof significant advantages, including:

-   -   higher productivity and lower investment: vessels can be        operated for prolonged periods of time under full load, meaning        that for equal production volume smaller vessels are needed than        in a batch process;    -   constant and better quality: process is easier to control due to        possibility of adapting process parameters to local and        instantaneous requirements and because steady-state-conditions        are much more stable;    -   high hygienic standard: continuous process is operated in a        closed system.    -   less energy: energy consumption is evenly spread, without major        use peaks;    -   less labour: operation of continuous process requires less        attention    -   less standstill and cleaning: continuous process can be operated        at much longer runlengths than batch processes.

U.S. Pat. No. 3,171,746 describes a continuous method of producing wortusing a double decoction process in which a mash is prepared in amixer-separator from malt and water and separated in a thick mash and athin mash. The thick mash is subjected to temperature conditions suchthat proteolysis and saccharification will occur, whereas the thin mash,which is rich in enzymes, is decocted and then reunited with the thickmash after the thick mash has completed the proteolytic andsaccharification actions.

DE-A 18 14 377 describes a double decoction process for the continuousproduction of wort wherein a mash is prepared by combining malt andwater and wherein part of the mash is fed to a vessel in which it issubjected to heat treatment before it is recombined with the remainderof the mash that has not been subjected to such heat treatment. Next,again a part of the mash is fed to a vessel in which it is heatprocessed before being combined with the remainder of the mash that hasnot been heat treated, following which the mash is separated in wort andspent grain.

WO 92/12231 describes a process for the continuous preparation of wortcomprising continuous enzymatic conversion of malt in at least onerotating disc contactor. In the example of this patent application adecoction suspension containing maize and malt is maintained at 50° C.for 5 minutes, heated to 95° C. for 10-15 minutes in a rotating disccontactor, combined with malt/water mixture, following which theresulting mixture is first heated to 65° C. for 30 minutes and then to76° C. for 5 minutes. In this process gelatinisation and enzymaticdegradation of the starch contained in the decoction suspension areachieved in a single heat treatment (i.e. 95° C. for 10-15 minutes).

As mentioned herein before, decoction mashing can advantageously be usedto produce mash extracts from malt and starch-containing adjuncts.Hence, it would be beneficial if a continuous decoction mashing methodcould be made available that can suitably be used for producing a mashextract from malt and one or more starch-containing adjuncts.

SUMMARY OF THE INVENTION

The present inventors have designed a method for continuously producinga mash extract by means of decoction mashing, which method offers theadvantage that it can be used to produce a high quality mash extractwhilst employing substantial amounts of starch-containing adjuncts suchas rice, maize, sorghum, barley, wheat and/or rye. The presentcontinuous method is characterised in that it comprises the followingsteps:

-   a. mixing a first malt enzyme source with water to obtain an aqueous    malt enzyme suspension;-   b. separately, mixing a second enzyme source with one or more    starch-containing adjuncts to obtain a decoction suspension whilst    maintaining temperature conditions that do not cause significant    gelatinisation of the starch;-   c. subjecting the decoction suspension to a first heat treatment at    60-85° C. to simultaneously partially gelatinise and enzymatically    degrade the starch;-   d. subjecting the decoction suspension to a second heat treatment at    a higher temperature than the first heat treatment to gelatinise the    starch at an increased rate and to a higher extent;-   e. combining the heated decoction suspension obtained from the    second heat treatment with the aqueous malt enzyme suspension from    step a. to obtain a mash;-   f. maintaining the mash at 35-85° C. for at least 20 minutes; and-   g. removing spent grain from the heated mash to produce a mash    extract.

In the present method the decoction suspension containing the one ormore adjuncts is subjected to a carefully controlled multi-step heattreatment. During this multi-step heat treatment, the starch-containingadjuncts are gelatinised by boiling, following which they can behydrolysed effectively by the amylases contained in the aqueous maltenzyme suspension with which the heated decoction suspension is(re)combined. During the relatively mild first heat treatment conditionsare chosen such that the rate of starch gelatinisation is in pace withthe rate of starch hydrolysis, meaning that the viscosity of thedecoction suspension is maintained at sufficiently low level to keep thesuspension pumpable. During the much more severe second heat treatment,the starch is gelatinised rapidly, making it much more susceptible toenzymatic hydrolysis, which is initiated when the decoction isrecombined with the aqueous malt enzyme suspension. Prior to themultistep heat treatment, the temperature is controlled in such a waythat significant gelatinisation is prevented and the viscosity is keptat a low level to ensure suitable transport conditions from the mixingvessel to the pump. The present method is very robust and easy tocontrol. Furthermore, the method yields a mash extract of constantquality.

DETAILED DESCRIPTION OF THE INVENTION

Accordingly, the present invention relates to a continuous method ofproducing a mash extract by decoction mashing, said method comprising:

-   a. mixing a first malt enzyme source with an aqueous liquid to    obtain an aqueous malt enzyme suspension;-   b. separately, mixing a second enzyme source with one or more    starch-containing adjuncts to obtain a decoction suspension whilst    maintaining temperature conditions that do not cause significant    gelatinisation of the starch;-   c. subjecting the decoction suspension to a first heat treatment at    60-85° C. to simultaneously partially gelatinise and enzymatically    degrade the starch;-   d. subjecting the decoction suspension to a second heat treatment at    a higher temperature than the first heat treatment to gelatinise the    starch at an increased rate and to a higher extent;-   e. combining the heated decoction suspension obtained from the    second heat treatment with the aqueous malt enzyme suspension from    step a. to obtain a mash;-   f. maintaining the mash at 35-85° C. for at least minutes; and-   g. removing spent grain from the heated mash to produce a mash    extract.

Preferably, each of the aforementioned steps a. to g. is conducted in acontinuous faction, as illustrated in the examples.

The term ‘adjunct’ as used herein encompasses any cereal grain orfermentable ingredient that can be added to the mash as a source ofstarch. The adjunct may be malted or unmalted, the latter beingpreferred. The adjuncts may optionally be pre-processed by e.g.torrification, flaking, cooking, micronisation, roasting. Rice, maize,sorghum, rye, oats, wheat, corn, tapioca flour, potato, malt, barley andcombinations thereof can be used for this purpose. Preferably, theadjunct is derived from a cereal selected from the group consisting ofrice, maize, sorghum, barley, rye and combinations thereof. Typically,the adjunct employed in the present method contains at least 60%,preferably at least 70% and more preferably at least 75% of starch byweight of dry matter.

In the present method malt may suitably be used as a source of maltenzymes. However, the present invention also encompasses the use ofcommercial enzyme preparations containing starch degrading enzymes suchas those found in malt, notably α-amylase, β-amylase and/orglucoamylase. Furthermore, it is within the scope of the presentinvention to employ both malt and commercial enzyme preparation, e.g.malt in the preparation of the aqueous malt enzyme suspension andcommercial enzymes in the preparation of the decoctions suspension.Preferably, the malt enzymes are employed in the present method in theform of malt.

In accordance with a particularly preferred embodiment of the invention,part of the aqueous malt enzyme suspension prepared in step a. isemployed as the second enzyme source in step b. Even more preferably,1-50 wt. % of the aqueous malt enzyme suspension prepared in step a. isemployed as the second enzyme source in step b. and the remainder of theaqueous malt enzyme suspension is combined with the heated decoctionsuspension obtained from the second heat treatment.

The present invention encompasses a method in which the aqueous maltenzyme suspension is separated in two malt enzyme suspensions that havedifferent solids contents, e.g. a thick and a thin mash suspension.Preferably, however, the composition of the aqueous malt enzymesuspension of step a. and the second enzyme source of step b. isidentical. Typically, the solids content of the malt enzyme suspensionsemployed in the present process is within the range of 200-500 g/l,preferably within the range of 250-350 g/l.

The benefits of the present method are most pronounced when asubstantial fraction of the fermentable sugars in the mash extract areprovided by the one or more adjuncts. Accordingly, in a preferredembodiment at least 5 wt. %, preferably from at least 10 wt. % and morepreferably 20-90 wt. % of the fermentable sugars contained in the mashextract originate from the one or more starch-containing adjuncts.

In the present method the decoction suspension is prepared whilstmaintaining temperature conditions that do not cause significantgelatinisation of the starch. More preferably these temperatureconditions do not cause gelatinisation of the starch. Advantageously,the aforementioned temperature conditions are maintained until the firstheat treatment.

As mentioned herein before, the conditions during the first heattreatment are relatively mild in order to ensure that the rate ofgelatinisation remains relatively low and to enable enzymaticdegradation of the starch. The partial hydrolysis of the starch duringthe first heating step counteracts the viscosity increase that normallyaccompanies starch gelatinisation. Thus, the viscosity increase observedduring the first and second heating step may be controlled so as not toexceed the levels that would make the suspension non-pumpable.Typically, the viscosity of the decoction suspension up till the secondheat treatment does not exceed 10 Pa.s. Preferably, said viscosity doesnot exceed 5 Pa.s, more preferably it does not exceed 1 Pa.s. Wheneverreference is made herein to viscosities, said viscosities are determinedusing measured pressure differences over defined pipe diameters and flowconditions (pipe diameter: 25 mm; pipe length: 5 m; flow rate 200 l/hr,assuming Newtonian fluid behaviour).

The heating conditions needed to gelatinise starch during the first andsecond heat treatment very much depend on the nature of the starch.Certain starches, such as barley starch, start to gelatinise atrelatively low temperatures, e.g. 55-62° C. Other starches, such as ricestarch, are much more stable towards gelatinisation and will notgelatinise significantly below temperature of 70-80° C. Consequently,the heating conditions to be employed in the first and second heatingstep need to be tailored to the type of starch present in the decoctionsuspension.

Typically, the first heat treatment in the present method advantageouslyinvolves heating the decoction suspension to within a temperature rangeof 65-82° C., preferably to within a temperature range of 65-80° C. Theduration of the first heat treatment preferably is within the range of1-30 minutes, more preferably within the range of 2-15 minutes.

Individual starch granules are known to gelatinise over a temperatureinterval. As temperature increases more starch granules gelatinise. Withfurther increasing temperature the starch granules begin to break downand at peak viscosity the rate of break down starts to exceedgelatinisation and resulting viscosity begins to drop off. In thepresent method, the decoction suspension reaches its peak viscosityduring the second heat treatment. Typically, the viscosity of thedecoction suspension after the second heat treatment does not exceed 30Pa.s. Preferably, said viscosity does not exceed 10 Pa.s and morepreferably, said viscosity does not exceed 1 Pa.s. These viscosities aredetermined in the same way as described herein before.

The second heat treatment of the decoction suspension advantageouslyinvolves heating to within a temperature range of 85-120° C., morepreferably to within a temperature range of 100-120° C. The duration ofthe second heat treatment preferably is within the range of 1-30minutes, more preferably within the range of 2-15 minutes.

According to a particularly preferred embodiment, the first and thesecond heat treatment of the decoction suspension comprise steaminjection. Steam injection offers the advantage that a rapid temperatureincrease can be realised without the risk of fouling of the heatexchange surface. It is preferred not to employ a rotating disccontactor as described in WO 92/12231 in the first heat treatment of thepresent method. Likewise, it is preferred to not employ this device inthe second heat treatment.

In accordance with yet another preferred embodiment the decoctionsuspension is cooled to a temperature of 60-100° C. after the secondheat treatment and prior to being combined with the aqueous malt enzymesuspension. By cooling the hot decoction suspension before it iscombined with the aqueous malt enzyme suspension the temperature of theresulting mash can be controlled effectively.

In the present method the decoction suspension is prepared by mixing thesecond enzyme source with one or more starch-containing adjuncts.Advantageously in the preparation of the decoction suspension additionalwater is admixed. Typically, the decoction suspension has a solidscontent within the range of 200-500 g/l, preferably within the range of220-400 g/l. According to a particularly preferred embodiment, thesolids content of aqueous malt enzyme suspension and the decoctionsuspension is maintained within the range of 250-350 g/l.

Following the second heat treatment, the mash obtained after recombiningthe decoction suspension and the aqueous malt enzyme suspension is keptunder conditions that favour enzymatic hydrolysis of the gelatinisedstarch. During this part of the present method starch is converted tofermentable sugars in two stages, liquefaction and saccharification.Liquefaction involves the breakdown of starch to complex sugars(dextrins) under the influence of e.g. α-amylase. When the liquefactionstage is complete, the mash has become much less viscous.Saccharification, or the breakdown of complex sugars to fermentablesugars occurs under the influence of enzymes such as glucoamylases andβ-amylase. Typically, liquefaction and saccharification are achieved inthe present method by maintaining the mash at a temperature within therange of 35-85° C., preferably within the range of 40-80° C. In order toachieve adequate conversion of starch into fermentable sugars, usually aresidence time at the aforementioned temperatures of at least 20 minutesis required. Preferably, the residence time applied at thesetemperatures is within the range of 30-120 minutes, more preferablywithin the range of 40-110 minutes.

The present method may suitably employ tap water or spring water in thepreparation of the aqueous malt enzyme suspension and/or the decoctionsuspension. According to a particularly preferred embodiment, however,the aqueous liquid used to produce the aqueous malt enzyme suspension,and preferably also the decoction suspension, is a recirculated washwater stream from the mash extract production. The use of such arecirculated wash water stream offers the advantage that it enables highextraction yields without the need of using large quantities of water.At the same time, recirculation makes it possible to achieve such highextraction yields whilst at the same time producing a high gravity mashextract.

Accordingly, a particularly advantageous embodiment of the presentinvention the mash extract is produced by:

-   a. transferring the heated mash into a first separator for    separation into mash extract and spent grain;-   b. transferring the spent grain into a first mixing vessel and    mixing it with sparging water;-   c. transferring the mixture of spent grain and sparging water into a    second separator to remove spent grain;-   d. recirculating an aqueous stream from the second separator to the    production of the aqueous malt enzyme suspension.

The term “separator” as used herein encompasses any device that cansuitably be used to separate solids from liquids. Examples of separatorsthat may suitably be used in the present method include: centrifuges,decanters, sedimentors, hydrocyclones, sieves, filters, membranes andpresses. Naturally, combinations of different types of separators (e.g.decanters and sieves) may be employed in the present method. Preferably,the separators employed in the present process are selected from thegroup consisting of centrifuges, decanters and sieves. More preferably,the separators employed are selected from the group consisting ofdecanters and centrifuges. Most preferably, the separators employed aredecanters.

It should be understood that wherever reference is made to a firstseparator, a second separator, a third separator etc., such first,second or third separator may actually comprises two or more separatingdevices that together perform the action of separating solids andliquid. These two or more separating devices may be operated in paralleland/or in series. For instance, it may be advantageous to employ aseparator that consists of a series of sieves, wherein the pore size ofthe sieves decreases in the downstream direction. Likewise it can beadvantageous to employ a sequence of centrifuges and/or decanter,wherein the centrifugal force applied increases in the downstreamdirection. It can also be advantageous to operate a number of separatingdevices in parallel, in particular if the process is operated in acontinuous fashion. When run in parallel well below full capacity,failure or shutdown of one separating device does not necessitateinterruption of the mash extraction process, meaning that the processcan be operated uninterruptedly for prolonged periods of time.

In case two or more separating devices are operated in parallel, thegravity of the mash extract obtained from the separator refers to theweight averaged gravity of the mash extracts obtained from the two ormore separating devices that make up the separator. In case two or moreseparating devices are operated in series, the gravity of the extractobtained from the separator refers to gravity of the extract obtainedfrom the last separating device.

Just like the separators, also the mixing vessels employed in thepresent process may actually consist of two or more mixing devices thatare operated in series or in parallel.

The use of recirculated wash water as described herein before enablesthe preparation of a high gravity mash extract, e.g. a mash extract witha gravity of 15° P. or more. This particular embodiment of the presentmethod can attain very high efficiencies in terms of energy consumptionand extraction yields. Furthermore, it can achieve an extremely highproductivity in the operation of the brewhouse.

The advantages of the present method are particularly pronounced in casethe gravity of the mash extract obtained from the first separatorexceeds 18° P. More preferably the gravity of the mash extract exceeds20° P., even more preferably it exceeds 25° P. In an especiallypreferred embodiment the gravity of the mash extract obtained from thefirst separator exceed 28° P., most preferably it exceeds 30° P.

Unexpectedly, it was found that despite the high gravity of the mashextract obtained in the present method, the extract loss observed in themethod is typically less than 5 wt. %, preferably less than 4 wt. %,more preferably less than 3 wt. %, most preferably less than 2 wt. %.Preferably, the latter efficiencies are realised across the completewort production process, including both mash separation and trubseparation. The amount of extract loss in the production of a mashextract may suitably be determined by measuring the extractconcentration in the liquid phase of the spent grain by a standardmethod for determining extract concentrations in wort (E.g. densitymeasurement by Anton Paar). Because of the absence of free liquid indewatered spent grains, said spent grains are conveniently extractedwith hot water, following which the exhausted spent grains are separatedby filtration. The extract losses can be calculated from the measuredextract level in the extraction liquid, taking into account the amountof water added.

In particular if the present method employs a sequence of three or moreseparators, extract losses can be minimised very effectively.Accordingly, a preferred embodiment of the invention relates to a methodas defined herein before, said method further comprising:

-   a. transferring the spent grain obtained from the second separator    into a second mixing vessel and mixing it with sparging water;-   b. transferring the mixture of spent grain and sparging water into a    third separator to remove spent gain; and-   c. recirculating the aqueous stream from the third separator as    sparging water to the first mixing vessel.

The gravity of the aqueous stream obtained from the second separatortypically is in the range of 1-10° P., preferably in the range of 1-8°P. The gravity of the aqueous stream obtained from the third separatoris typically very low, indicating that the spent grain is essentiallyexhausted. Preferably, the gravity of the aqueous stream from the thirdseparator is in the range of 0.1-2° P., more preferably in the range of0.1-1.5° P. The gravities realised in the aqueous streams obtained fromthe second and third separator are strongly dependent on the extractconcentration achieved in the primary mash extract.

In order to produce a high gravity mash extract with minimum extractlosses it is preferred to recirculate the complete aqueous streamobtained from the second separator to the mashing step. In the mashingstep, besides the aqueous stream from the second separator, also aqueousstreams generated downstream of the brewhouse, e.g. from yeast washing,may be employed. Typically, the recirculated aqueous stream from thesecond separator constitutes at least 80 wt. %, preferably at least 90wt. % of the total liquid employed in the mashing step. Most preferably,the recirculated aqueous stream from the second separator provides allthe mashing liquid that is used in the mashing step.

The invention is further illustrated by means of the following examples.

EXAMPLES Example 1

A stream of 136 kg/hr hammer milled malt grist is closed into a 70 lcontinuous stirred tank reactor and mixed with 313 kg/hr brewing waterat a temperature of 50° C. Hereafter, part of the mixture, referred toas ‘mash’, is fed (340 l/hr) into a vertical cylindrical plug flowreactor. This malt mash stream provides the necessary enzymes (starchdegrading amylases) to reduce the viscosity during heat treatment in thereactor. The reactor type used has been described in earlier patents byHeineken (WO 92/12231). The remaining part of the mash is pumped into a50 l continuous stirred tank reactor in which a stream of 59 kg/hr ofmaize grits is dosed together with 140 kg/hr of water. The combinedstreams have a temperature of 50° C. which is well below thegelatinisation temperature of the maize starch. To gelatinise andliquefy the starch in the maize by enzymatic action, the suspension ofmalt mash, maize grits and water is subjected to direct steam injectionand the temperature is raised to 78° C. At this temperature, asignificant amount of the starch is gelatinised but also liquefied bythe malt enzymes. Without these enzymes, the starch immediately forms athick paste and clogs up the equipment. After this first temperatureincrease, the enzymes are allowed to act on the starch for 5 min in aplug flow reactor of 1 meter in length. Subsequently, another directsteam injection treatment follows which raises the temperature to 100°C. and the starch granules are fully gelatinised by a rest at thistemperature for 5 min in a similar plug flow reactor.

The stream containing fully gelatinized starch granules (decoctionstream) is now also pumped in the aforementioned stirred plug flowreactor in which it is combined with the malt mash stream. The decoctionstream, having a temperature of 100° C., is combined with the malt mashstream, having a temperature of 50° C., yielding a total mash stream,having a temperature of 65° C. A heating jacket is used to control thesaccharification temperature at 67° C. At the top of the column, themash is heated by a heating jacket to a temperature of 78° C. and thetotal reactor is insulated to minimise heat losses. The mash has a totalresidence time inside the column of 65 minutes and the resulting mash isfed into the mash separation section.

Separation of the malt husks and other solids from the mash is done bytwo decanters. These decanters are scroll type bowl centrifuges with acontinuous discharge of clarified liquid and thickened spent grains. Thefirst decanter operates at a rotational speed of 3500 rpm and adifferential screw speed of 2 rpm. This decanter has a theoreticalcapacity factor value of 1700 m².

The theoretical capacity factor (SIGMA value) of a decanter iscalculated according to the following relation between: the length ofthe cylindrical bowl (L), the gravitational acceleration (g), theangular speed (ω), the radius of the dam ring or overflow ring (r₁) andthe radius of the cylindrical bowl (r₂).

$\Sigma = {\frac{\varpi^{2}}{g}\pi \; {L\left( {{\frac{3}{2}r_{2}^{2}} + {\frac{1}{2}r_{1}^{2}}} \right)}}$

The product (mash extract) is discharged from the first decanter to thenext unit operation (boiling) and the spent grains are released into asmall continuous stirred tank reactor. In the latter, 506 l/hr washingwater of 80° C. is applied and with a residence time of 13 minutes,spent grains particles and water are homogeneously mixed.

The liquid phase of the resulting mixture is separated by a seconddecanter operating at 2 rpm differential screw speed, 4000 rpm and atheoretical capacity factor of 1800 m². The clarified liquid supernatantis recirculated and mixed with the outlet of the mashing column and thismixture is the feed of the first decanter. The product stream from thefirst decanter has an extract concentration of 14.8° P. Both decanterswere equipped with a centrifugal fan and consequently work as a pump onthe supernatant outlet.

The product from the mash separation is now referred to as wort and hasa flow rate of 1030 kg/hr. Hop extract is dosed continuously in-line ata rate of 140 g/hr and the mixture is heated to a temperature of 102° C.by direct steam injection. By the positive head of the first decanter,the wort is pumped into a plug flow reactor. This column reactor has thesame characteristics as the earlier described mashing conversion column.The volume of this reactor is 1 m³ and the residence time is 60 min.Typical reactions taking place in this reactor are: protein denaturationand coagulation, sterilisation, hop isomerisation, colour formation,dimethylsulphide (DMS) production from its malt-based precursor(S-methylmethionine).

The wort is thereafter treated in a sieve-plate geometry strippingcolumn earlier described in Heineken patent (WO 95/26395). Steam of 1.5bar is used in counter current operation to remove undesirable flavourcompounds (mainly DMS) at a flow rate of 15 kg/h and at atmosphericconditions at the top of the stripper. The wort leaving the bottom ofthe stripper is fed into a small buffer with negligible dimensions anddirectly ted into a centrifuge of the discontinuous discharge type. Thismachine has a rotational speed of 7400 rpm and a theoretical capacityfactor of 13000 m².

The theoretical capacity factor of a centrifuge is calculated on thebasis of the method described in “Solid-Liquid Separation”, 2^(nd)edition, 1981, by Ladislav Svarovsky, Butterworth-Heineman. The factoris calculated according to the following relation between: the number ofdiscs (n), the gravitational acceleration (g), the angular speed (ω),the angle of the discs with the vertical feed pipe (α), the inner radiusof the discs package (r₁) and the outer radius of the discs package(r₂).

$\Sigma = {\frac{\varpi^{2}}{g}\frac{2}{3}\pi \; {n\left( {r_{2}^{3} - r_{1}^{3}} \right)}\cot \; \alpha}$

Next, cooling of the wort takes place in two parallel plate and framewort coolers that lower the wort temperature from 95-100° C. to 8° C. bya two stage water-glycol set-up.

A total volume of 2.2 m³ cooled wort is continuously fed into acylindrical/conical fermentation tank together with active yeast in aconcentration of 2.5 g/l. Continuous oxygenation is achieved by in-lineaeration. The primary batch fermentation was performed at 10° C. andwhen the extract concentration reached 6.5° P., temperature was allowedto increase to 13° C. After the diacetyl concentration was reduced to alevel of 30 ppm, the contents of the tank were cooled to −1.5° C. in 24hours. This cold phase was maintained for 6 days.

The beer was then filtered over a kieselguhr bright beer filter of thevertical disc type. After this filtration, the beer is stabilised withthe usual dosings of PVPP and the necessary PVPP filtration. Finally,the beer was packaged in suitable containers (glass bottle).

Example 2

A stream of 120 kg/hr hammer milled malt grist is dosed into a 70 lcontinuous stirred tank reactor and mixed with 240 kg/hr brewing waterat a temperature of 50° C. Hereafter, part of the mixture, referred toas ‘mash’, is fed into the vertical cylindrical plug flow reactordescribed in Example 1.

Unmalted adjunct in the folio of rice grits at a flow rate of 100 kg/hrare dosed into a 50 l continuous stirred tank reactor in which a streamof 210 kg/hr of water is added. A stream of heat resistant starchdegrading amylolytic enzymes is dosed to reduce the viscosity insubsequent heat treatment. The resulting mixture had a temperature of50° C. which is well below the gelatinisation temperature of the ricestarch. To gelatinise and liquefy the starch in the rice by enzymaticaction, the suspension of rice grits, enzymes and water is subjected todirect steam injection and the temperature is raised to 78° C. At thistemperature, a significant amount of the starch is gelatinised but alsoliquefied by the amylolytic enzymes. Without the enzymes, the starchimmediately forms a thick paste and clogs up the equipment. After thisfirst temperature increase, the enzymes are allowed to act on the starchfor 5 min in a plug flow reactor of 1 meter in length. Subsequently,another direct steam injection treatment follows which raises thetemperature to 100° C. and the starch granules are fully gelatinised bya rest at this temperature for 5 min in a similar plug flow reactor. Toachieve the proper saccharification temperature (67° C. in this example)upon mixing with the malt mash, the decoction stream is cooled to asuitable temperature in a shell and tube heat exchanger.

This cooled stream is also pumped into the aforementioned stirred plugflow reactor, where it is combined with the malt mash stream. A heatingjacket is used to control the saccharification temperature at 67° C. Atthe top of the column, the mash is heated by a heating jacket to atemperature of 78° C. and the total reactor is insulated to minimiseheat losses. The mash has a total residence time inside the column of 60minutes and the resulting mash is fed into the mash separation section.

Separation of the malt husks and other solids from the mash is done bytwo decanters. These decanters are scroll type bowl centrifuges with acontinuous discharge of clarified liquid and thickened spent grains. Thefirst decanter operates at a rotational speed of 3500 rpm and adifferential screw speed of 3 rpm. This decanter has a theoreticalcapacity factor value of 1700 m². The product (mash extract) isdischarged from the first decanter to the next unit operation (boiling)and the spent grains are released into a small continuous stirred tankreactor. In the latter, 510 l/hr washing water of 80° C. is applied andwith a residence time of 13 minutes, spent grains particles and waterare homogeneously mixed.

The liquid phase of the resulting mixture is separated by a seconddecanter operating at 3 rpm differential screw speed, 4000 rpm and atheoretical capacity factor of 1800 m². The clarified liquid supernatantis recirculated and mixed with the mash from the mashing column prior toentry of the first decanter. The product stream from the first decanterhas an extract concentration of 16.4° P. Both decanters were equippedwith a centrifugal fan and consequently work as a pump on thesupernatant outlet.

The product from the mash separation is now referred to as wort and hopextract is dosed continuously in-line at a rate of 120 g/hr and themixture is heated to a temperature of 102° C. by direct steam injection.By the positive head of the first decanter, the wort is pumped into aplug flow reactor. This column reactor has the same characteristics asthe earlier described mashing conversion column. The volume of thisreactor is 1 m³ and the residence time is 60 min. Typical reactionstaking place in this reactor are: protein denaturation and coagulation,sterilisation, hop isomerisation, colour formation, dimethylsulphide(DMS) production from its malt-based precursor (S-methylmethionine).

The wort is thereafter treated in a sieve-plate geometry strippingcolumn earlier described in Heineken patent (WO 95/26395). Steam of 1.5bar is used in countercurrent operation to remove undesirable flavourcompounds (mainly DMS) at a flow rate of 15 kg/h and at atmosphericconditions at the top of the stripper. The wort leaving the bottom ofthe stripper is fed into a small buffer with negligible dimensions anddirectly fed into a centrifuge of the discontinuous discharge type. Thismachine has a rotational speed of 7400 rpm and a theoretical capacityfactor of 13000 m². Analysis of the wort showed that the finalattenuation limit is 82-83%.

Next, cooling of the wort takes place in two parallel plate and framewort coolers that lower the wort temperature from 95-100° C. to 8° C. bya two stage water-glycol set-up.

A total volume of 2.2 m³ cooled wort is continuously fed into acylindrical/conical fermentation tank together with active yeast in aconcentration of 2.5 g/l. Continuous oxygenation is achieved by in-lineaeration. The primary batch fermentation was performed at 10° C. andwhen the extract concentration reached 6.5° P., temperature was allowedto increase to 13° C. After the diacetyl concentration was reduced to alevel of 30 ppm, the contents of the tank were cooled to −1.5° C. in 24hours. This cold phase was maintained for 6 days.

The beer was then filtered over a kieselguhr bright beer filter of thevertical disc type. After this filtration, the beer is stabilised withthe usual dosings of PVPP and the necessary PVPP filtration. Finally,the beer was packaged in suitable containers (glass bottle).

Example 3

A stream of 4.5 m³/hr of wort is produced with an extract concentrationof 18° P. at the end of the wort production process, using a combinationof malt grist and unmalted maize grits. This wort is fermented andmatured in continuous fermentors and subsequently stabilised in batchstorage tanks, separated in a centrifuge and filtered on a bright beerfilter. A detailed description of the brewing process is provided below.

At the front of the process, 1620 l/hr of brewing water (47° C.) iscontinuously mixed with 720 kg/hr malt grist. This malt grist wasproduced by a hammer mill equipped with a 2.5 mm screen. Both streamsare fed into a continuous stirred tank reactor of 80 l working volume ata temperature of 45° C. Part of the resulting malt mash stream isdirected to a subsequent plug flow mashing column, similar to the onedescribed in Example 1. The other part (250 l/hr) of the malt mashstream is fed into a parallel process that enables the usage of unmaltedmaize grits as adjunct for the final beer product.

In this continuous decoction process, unmalted maize grits (350 kg/h)are fed into a continuous stirred tank reactor together with a stream ofbrewing water (790 kg/h) of 52° C. and the abovementioned stream of maltmash. The resulting temperature in this 120 l vessel on combination ofthe streams is 50° C. which is sufficiently low to prevent excessivegelatinisation of the maize starch and the related viscosity increase.The mixture is pumped to a first holding column via a direct steaminjection point. Steam is injected to elevate the temperature of thedecoction stream to 75-78° C. and part of the maize starch isgelatinised. However, due to the presence of a portion of the malt mashthe amylases from the malt break up the polymeric starch strains andlower the viscosity. The residence time of 15 min at the specifiedtemperature enables the viscosity to be reduced to a level where anothertemperature increase to 100° C. can be applied without causingunacceptably high viscosities. This second step is done by anotherdirect steam injection and a 5 min residence in a simple plug flowreactor. The resulting gelatinised mixture is cooled to 90° C. andsubsequently fed into the mashing column where it is combined with theseparated malt mash stream, producing a mixed stream having atemperature that is optimal for amylase activity and the completeconversion of starch of malt and maize to sugars.

The cylindrical plug flow reactor for the mashing process has beendescribed in earlier patents by Heineken (WO 92/12231). At certainheights in the top of the column, the mash is heated by direct steaminjection. Temperatures are chosen such that the conversion of maltstarch to fermentable sugars is appropriate for the product desired.Present temperature profile has a saccharification rest at 66° C. and amashing off temperature of 76° C. The mash has a residence time of 80minutes and the resulting mash is fed into the mash separation section.

The mash separation section consists of two scroll type bowl centrifugeswith a continuous discharge of clarified liquid and thickened spentgrains, known generally as decanters. The first decanter operates at arotational speed of 3650 rpm, a differential screw speed of 10 rpm and atheoretical capacity factor of 6200 m². The product (mash extract) isdischarged from the first decanter to the next unit operation (boiling)and the spent grains are released into a small continuous stirred tankreactor. In the latter, 1150 l/hr washing water of 72° C. is appliedand, with a residence time of 2 minutes, a homogeneous suspension isachieved. The liquid phase of the resulting mixture is separated by asecond decanter operating at a rotational speed of 4000 rpm, adifferential screw speed of 20 rpm and a theoretical capacity factor of2600 m². The clarified liquid supernatant is recirculated and combinedwith the exit flow from the mashing column. This lowers the extractconcentration in the feed of the first decanter to about 17° P. Thespent grains from the second decanter are discharged to a silo. Bothdecanters were equipped with a centrifugal fan and consequently work asa pump on the supernatant outlet.

The product from the mash separation is now referred to as wort and hasa flow rate of 4.5 m³/hr. Hop extract is dosed in-line at a rate of 32g/hr and the mixture is heated to a temperature of 105° C. by directsteam injection. By the positive head of the first decanter, the wort ispumped into a plug flow reactor. This column reactor has the samecharacteristics as the earlier described mashing conversion column, butthe height is proportionally increased with the increased flow rate inthis part of the process. The residence time is therefore 67 min.Typical reactions taking place in the reactor are: protein denaturationand coagulation, sterilisation, hop isomerisation, colour formation,dimethylsulphide (DMS) production from its malt-based precursor(S-methylmethionine).

The wort is thereafter treated in a sieve-plate geometry strippingcolumn earlier described in Heineken patent (WO 95/26395). Steam of 1.5bar is used in countercurrent to remove undesirable flavour compounds(mainly DMS) at a flow rate of 100 kg/hr and at atmospheric conditions.The wort leaving the bottom of the stripper is fed into a small bufferwith negligible dimensions and directly fed into a centrifuge of thediscontinuous discharge type. This machine has a rotational speed of7400 rpm and a SIGMA value of 70000 m².

Cooling of the wort takes place by two parallel plate and frame wortcoolers that lower the wort temperature from 95-100° C. to 4° C. by atwo stage water-glycol set-up.

Cooled wort is fed into the first stirred fermentation vessel with a networking volume of 14 m³. The vessel is operated at a temperature of 10°C. and under aerobic conditions by the continuous addition of an aeratedrecirculated stream from the downstream end of the process, containingthickened yeast as the main constituent besides water. The gravity inthis vessel is 13° P. The yeast necessary for the fermentation is addedin the form of the abovementioned recirculated stream.

The fermentation broth from the first fermentation vessel is transferredto the second vessel. This vessel has a working volume of 160 m³ and iskept at a temperature of 13° C. by wall cooling. The original gravity inthis vessel is 7° P. and the yeast concentration is 80 g wet yeast/l.The outlet of this vessel is split into two streams: one part (2.5m³/hr) is combined with another stream from the end of the process andrecirculated to the first fermentation vessel, whereas the other part(5.3 m³/hr) is fed into a third fermentation vessel.

This third vessel has a working volume of 140 m³ and the contents havean original gravity of 3.5° P. The product of this vessel is transferredto a yeast sedimentation vessel with a working volume of 7 m³. The yeastsedimentation vessel separates the main part of the yeast (90-95%) fromthe green beer. The compacted yeast in the bottom of the yeastsedimentation vessel has a yeast concentration of 200 g wet yeast/l.This stream is partly recirculated to the front of the fermentationprocess and partly sent to waste surplus yeast storage. The part of theyeast sent to surplus is controlled on the basis of the amount that isleaving the top of the yeast sedimentation vessel and the amount ofyeast grown in the fermentation vessels. Green beer from the top of theyeast sedimentation vessel is continuously fed into either batchmaturation tanks or into a continuous maturation vessel.

In case of the batch option, the working volume of the maturation tankis equal to the total volume of fermented wort produced in 24 hours. Thetemperature is allowed to raise to 15° C. by heat exchange in the pipetowards the maturation tank and/or natural fermentation heatdevelopment. This temperature favours conversion of acetolactate (ametabolic fermentation product) to diacetyl. Due to the presence ofyeast in this phase, the yeast can take up the diacetyl and convert itto acetoin or subsequent metabolites. The negative impact of diacetyl inthe beer is therewith removed and residual diacetyl levels are typicallydetermined to be <20 ppb. After the diacetyl reduction has reachedacceptable levels, the beer is cooled down to −1.5° C. and stored forseveral days. After this period, the beer is filtered over kieselguhrwith 80-100 g/1 kieselguhr as bodyfeed. Prior to filtration, the beer iscentrifuged with a disc type separator that operates at 70,000 m²theoretical capacity factor to remove total suspended solids with anefficiency of 95-98%. Typical filtration runs are performed on 6000-8000hl at a flow rate of 4-5.5 hl/m²/hr. After this filtration, the beer isstabilised with the usual dosings of PVPP and the necessary PVPPfiltration. Finally, the beer is packaged in any suitable container(bottle, keg, can).

When using a continuous maturation process, the green beer iscontinuously fed in the top of a 520 m³ vessel via a spray ball thatdistributes the beer over the surface area of the tank. In this example,the beer was heated from 13° C. to 15° C. with a shell and tube heatexchanger. This will accelerate the abovementioned conversion ofα-acetolactate formed during primary fermentation towards diacetyl. Theyeast will settle through the beer and will establish the abovementionedconversion of diacetyl and other vicinal diketones to acetoin andsubsequent metabolites. The beer has a residence time in this example of100 hours and the residual diacetyl levels are 7.3±2.3 ppb (95% Cl,n=6). The yeast settles at the conical bottom of the maturation tank andis removed and treated as rest beer. The matured beer is removed fromjust above the settled yeast cone and is transferred via a continuousheat exchanger towards batch cold storage tanks at a temperature of−1.5° C.

Cold storage tanks are filled in one day and thereafter, the beer isstored for at least 2 days at a temperature of −1.5° C. After thisstorage period, sedimented yeast is purged from the bottom of the tankand the remaining beer is separated over a disc type centrifuge asdescribed above. Directly after this treatment, the beer is filteredover a kieselguhr filter at a typical flow rate of at a flow rate of4-5.5 hl/m²/hr with a filtration run of on 6000-8000 hl.

After the beer has been stabilised by PVPP treatment, it is packaged inthe desired packaging materials (bottle, can, keg).

1. A method of producing a mash extract comprising: a. mixing a firstmalt enzyme source with an aqueous liquid to obtain an aqueous maltenzyme suspension; b. separately, mixing a second enzyme source with oneor more starch-containing adjuncts to obtain a decoction suspensionwhile maintaining temperature conditions that do not cause significantgelatinisation of the starch; c. subjecting the decoction suspension toa first heat treatment at 60-85° C. to simultaneously partiallygelatinise and enzymatically degrade the starch; d. subjecting thedecoction suspension to a second heat treatment at a higher temperaturethan the first heat treatment to gelatinise the starch at an increasedrate and to a higher extent; e. combining the heated decoctionsuspension obtained from the second heat treatment with the aqueous maltenzyme suspension from step a. to obtain a mash; f. maintaining the mashat 35-85° C. for at least 20 minutes; and g. removing spent grain fromthe heated mash to produce a mash extract.
 2. The method according toclaim 1, wherein part of the aqueous malt enzyme suspension prepared instep a. is employed as the second enzyme source in step b.
 3. The methodaccording to claim 1, wherein 1-50 wt. % of the aqueous malt enzymesuspension prepared in step a. is employed as the second enzyme sourcein step b. and the remainder of the aqueous malt enzyme suspension iscombined with the heated decoction suspension obtained from the secondheat treatment.
 4. The method according to claim 1, wherein at least 5wt. % of the fermentable sugars contained in the mash extract originatefrom the one or more starch-containing adjuncts.
 5. The method accordingto claim 1, wherein the composition of aqueous malt enzyme suspension ofstep a. and the second enzyme source of step b. is identical.
 6. Themethod according to claim 1, wherein the starch-containing adjunct isderived from a cereal selected from the group consisting of rice, maize,sorghum, rye, oats, wheat, corn, tapioca flour, potato, malt, barley andcombinations thereof.
 7. The method according to claim 1, wherein thestarch-containing adjunct is pre-processed by torrification, flaking,cooking, micronisation or roasting.
 8. The method according to claim 1,wherein the viscosity of the decoction suspension up till the secondheat treatment does not exceed 10 Pa.s.
 9. The method according to claim8, wherein the viscosity of the decoction suspension up till the secondheat treatment does not exceed 5 Pa.s.
 10. The method according to claim9, wherein the viscosity of the decoction suspension up till the secondheat treatment does not exceed 1 Pa.s.
 11. The method according to claim1, wherein the first and the second heat treatment of the decoctionsuspension comprise steam injection.
 12. The method according to claim1, wherein the decoction suspension is cooled to a temperature of60-100° C. after the second heat treatment and prior to being combinedwith the aqueous malt enzyme suspension.
 13. The method according toclaim 1, wherein the decoction suspension is prepared by mixing thesecond enzyme source with one or more starch-containing adjuncts andadditional water.
 14. The method according to claim 1, wherein the maltenzyme suspensions and the decoction suspensions have a solids contentmaintained within the range of 200-500 g/l.
 15. The method according toclaim 1, wherein the aqueous liquid used to produce the aqueous maltenzyme suspension and the decoction suspension is recirculated washwater stream from the mash extract production.